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Arithmetic (from the Greek ἀριθμός ''arithmos'', '
number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More un ...
' and τική έχνη ''tiké échne', ' art' or '
craft A craft or trade is a pastime or an occupation that requires particular skills and knowledge of skilled work. In a historical sense, particularly the Middle Ages In the history of Europe, the Middle Ages or medieval period lasted fr ...
') is a branch of
mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calculus, change (mathematical analysis, analysis). It has no generally ...
that consists of the study of
number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More un ...
subtraction Subtraction is an arithmetic operation that represents the operation of removing objects from a collection. Subtraction is signified by the minus sign, . For example, in the adjacent picture, there are apples—meaning 5 apples with 2 taken awa ...
,
multiplication Multiplication (often denoted by the cross symbol , by the mid-line dot operator , by juxtaposition, or, on computers, by an asterisk ) is one of the four elementary Operation (mathematics), mathematical operations of arithmetic, with the ...
, division, exponentiation and extraction of roots. Arithmetic is an elementary part of number theory, and number theory is considered to be one of the top-level divisions of modern mathematics, along with algebra, geometry, and mathematical analysis, analysis. The terms ''arithmetic'' and ''higher arithmetic'' were used until the beginning of the 20th century as synonyms for ''number theory'', and are sometimes still used to refer to a wider part of number theory.

# Arithmetic operations

The basic arithmetic operations are addition, subtraction, multiplication and division, although arithmetic also includes more advanced operations, such as manipulations of percentages, square roots, exponentiation, logarithmic functions, and even trigonometric functions, in the same vein as logarithms (prosthaphaeresis). Arithmetic expressions must be evaluated according to the intended sequence of operations. There are several methods to specify this, either—most common, together with infix notation—explicitly using parentheses and relying on Order of operations, precedence rules, or using a Polish notation, prefix or Reverse Polish notation, postfix notation, which uniquely fix the order of execution by themselves. Any set of objects upon which all four arithmetic operations (except division by zero) can be performed, and where these four operations obey the usual laws (including distributivity), is called a field mathematics, field.

Addition, denoted by the symbol $+$, is the most basic operation of arithmetic. In its simple form, addition combines two numbers, the addend, ''addends'' or ''terms'', into a single number, the summation, ''sum'' of the numbers (such as or ). Adding finitely many numbers can be viewed as repeated simple addition; this procedure is known as summation, a term also used to denote the definition for "adding infinitely many numbers" in an series (mathematics), infinite series. Repeated addition of the number one, 1 is the most basic form of counting; the result of adding is usually called the successor function, successor of the original number. Addition is commutative and associative, so the order in which finitely many terms are added does not matter. The 0 (number), number has the property that, when added to any number, it yields that same number; so, it is the identity element of addition, or the additive identity. For every number , there is a number denoted , called the ''opposite (mathematics), opposite'' of , such that and . So, the opposite of is the inverse element, inverse of with respect to addition, or the additive inverse of . For example, the opposite of is , since . Addition can also be interpreted geometrically, as in the following example. If we have two sticks of lengths ''2'' and ''5'', then, if the sticks are aligned one after the other, the length of the combined stick becomes ''7'', since .

## Subtraction

Subtraction, denoted by the symbol $-$, is the inverse operation to addition. Subtraction finds the ''difference'' between two numbers, the ''minuend'' minus the ''subtrahend'': Resorting to the previously established addition, this is to say that the difference is the number that, when added to the subtrahend, results in the minuend: For positive arguments and holds: :If the minuend is larger than the subtrahend, the difference is positive. :If the minuend is smaller than the subtrahend, the difference is negative. In any case, if minuend and subtrahend are equal, the difference Subtraction is neither Commutative property, commutative nor Associative property, associative. For that reason, the construction of this inverse operation in modern algebra is often discarded in favor of introducing the concept of inverse elements (as sketched under ), where subtraction is regarded as adding the additive inverse of the subtrahend to the minuend, that is, . The immediate price of discarding the binary operation of subtraction is the introduction of the (trivial) unary operation, delivering the additive inverse for any given number, and losing the immediate access to the notion of difference (mathematics), difference, which is potentially misleading when negative arguments are involved. For any representation of numbers, there are methods for calculating results, some of which are particularly advantageous in exploiting procedures, existing for one operation, by small alterations also for others. For example, digital computers can reuse existing adding-circuitry and save additional circuits for implementing a subtraction, by employing the method of two's complement for representing the additive inverses, which is extremely easy to implement in hardware (Inverter (logic gate), negation). The trade-off is the halving of the number range for a fixed word length. A formerly wide spread method to achieve a correct change amount, knowing the due and given amounts, is the ''counting up method'', which does not explicitly generate the value of the difference. Suppose an amount ''P'' is given in order to pay the required amount ''Q'', with ''P'' greater than ''Q''. Rather than explicitly performing the subtraction ''P'' − ''Q'' = ''C'' and counting out that amount ''C'' in change, money is counted out starting with the successor of ''Q'', and continuing in the steps of the currency, until ''P'' is reached. Although the amount counted out must equal the result of the subtraction ''P'' − ''Q'', the subtraction was never really done and the value of ''P'' − ''Q'' is not supplied by this method.

## Multiplication

Multiplication, denoted by the symbols $\times$ or $\cdot$, is the second basic operation of arithmetic. Multiplication also combines two numbers into a single number, the ''product''. The two original numbers are called the ''multiplier'' and the ''multiplicand'', mostly both are simply called ''factors''. Multiplication may be viewed as a scaling operation. If the numbers are imagined as lying in a line, multiplication by a number greater than 1, say ''x'', is the same as stretching everything away from 0 uniformly, in such a way that the number 1 itself is stretched to where ''x'' was. Similarly, multiplying by a number less than 1 can be imagined as squeezing towards 0, in such a way that 1 goes to the multiplicand. Another view on multiplication of integer numbers (extendable to rationals but not very accessible for real numbers) is by considering it as repeated addition. For example. corresponds to either adding times a , or times a , giving the same result. There are different opinions on the advantageousness of these Multiplication and repeated addition, paradigmata in math education. Multiplication is commutative and associative; further, it is distributivity, distributive over addition and subtraction. The multiplicative identity is 1, since multiplying any number by 1 yields that same number. The multiplicative inverse for any number except  is the reciprocal (mathematics), reciprocal of this number, because multiplying the reciprocal of any number by the number itself yields the multiplicative identity .  is the only number without a multiplicative inverse, and the result of multiplying any number and is again One says that is not contained in the multiplicative Group (mathematics), group of the numbers. The product of ''a'' and ''b'' is written as or . When ''a'' or ''b'' are expressions not written simply with digits, it is also written by simple juxtaposition: ''ab''. In computer programming languages and software packages (in which one can only use characters normally found on a keyboard), it is often written with an asterisk: a * b. Algorithms implementing the operation of multiplication for various representations of numbers are by far more costly and laborious than those for addition. Those accessible for manual computation either rely on breaking down the factors to single place values and applying repeated addition, or on employing Mathematical table, tables or slide rules, thereby mapping multiplication to addition and vice versa. These methods are outdated and are gradually replaced by mobile devices. Computers utilize diverse sophisticated and highly optimized algorithms, to implement multiplication and division for the various number formats supported in their system.

## Division

Division, denoted by the symbols $\div$ or $/$, is essentially the inverse operation to multiplication. Division finds the ''quotient'' of two numbers, the ''dividend'' divided by the ''divisor''. Any dividend division by zero, divided by zero is undefined. For distinct positive numbers, if the dividend is larger than the divisor, the quotient is greater than 1, otherwise it is less than or equal to 1 (a similar rule applies for negative numbers). The quotient multiplied by the divisor always yields the dividend. Division is neither commutative nor associative. So as explained in , the construction of the division in modern algebra is discarded in favor of constructing the inverse elements with respect to multiplication, as introduced in . Hence division is the multiplication of the dividend with the multiplicative inverse, reciprocal of the divisor as factors, that is, Within the natural numbers, there is also a different but related notion called Euclidean division, which outputs two numbers after "dividing" a natural (numerator) by a natural (denominator): first a natural (quotient), and second a natural (remainder) such that and In some contexts, including computer programming and advanced arithmetic, division is extended with another output for the remainder. This is often treated as a separate operation, the Modulo operation, denoted by the symbol $%$ or the word $mod$, though sometimes a second output for one "divmod" operation. In either case, Modular arithmetic has a variety of use cases. Different implementations of division (floored, truncated, Euclidean, etc) correspond with different implementations of modulus.

# Fundamental theorem of arithmetic

The fundamental theorem of arithmetic states that any integer greater than 1 has a unique prime factorization (a representation of a number as the product of prime factors), excluding the order of the factors. For example, 252 only has one prime factorization: :252 = 2 × 3 × 7 Euclid's Elements first introduced this theorem, and gave a partial proof (which is called Euclid's lemma). The fundamental theorem of arithmetic was first proven by Carl Friedrich Gauss. The fundamental theorem of arithmetic is one of the reasons Prime_number#Primality_of_one, why 1 is not considered a prime number. Other reasons include the sieve of Eratosthenes, and the definition of a prime number itself (a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers.).

# Decimal arithmetic

Decimal representation refers exclusively, in common use, to the written numeral system employing arabic numerals as the numerical digit, digits for a radix decimal, 10 ("decimal") positional notation; however, any numeral system based on powers of 10, e.g., Greek Numerals, Greek, Cyrillic numerals, Cyrillic, Roman numerals, Roman, or Chinese numerals may conceptually be described as "decimal notation" or "decimal representation". Modern methods for four fundamental operations (addition, subtraction, multiplication and division) were first devised by Brahmagupta of India. This was known during medieval Europe as "Modus Indoram" or Method of the Indians. Positional notation (also known as "place-value notation") refers to the representation or encoding of
number A number is a mathematical object used to counting, count, measurement, measure, and nominal number, label. The original examples are the natural numbers 1, 2, 3, 4, and so forth. Numbers can be represented in language with number words. More un ...

# Compound unit arithmetic

Compound unit arithmetic is the application of arithmetic operations to mixed radix quantities such as feet and inches; gallons and pints; pounds, shillings and pence; and so on. Before decimal-based systems of money and units of measure, compound unit arithmetic was widely used in commerce and industry.

## Basic arithmetic operations

The techniques used in compound unit arithmetic were developed over many centuries and are well documented in many textbooks in many different languages. In addition to the basic arithmetic functions encountered in decimal arithmetic, compound unit arithmetic employs three more functions: * Reduction (mathematics), Reduction, in which a compound quantity is reduced to a single quantity—for example, conversion of a distance expressed in yards, feet and inches to one expressed in inches. * Expansion, the inverse function to reduction, is the conversion of a quantity that is expressed as a single unit of measure to a compound unit, such as expanding 24 oz to . * Normalization is the conversion of a set of compound units to a standard form—for example, rewriting "" as "". Knowledge of the relationship between the various units of measure, their multiples and their submultiples forms an essential part of compound unit arithmetic.

## Principles of compound unit arithmetic

There are two basic approaches to compound unit arithmetic: * Reduction–expansion method where all the compound unit variables are reduced to single unit variables, the calculation performed and the result expanded back to compound units. This approach is suited for automated calculations. A typical example is the handling of time by Microsoft Excel where all time intervals are processed internally as days and decimal fractions of a day. * On-going normalization method in which each unit is treated separately and the problem is continuously normalized as the solution develops. This approach, which is widely described in classical texts, is best suited for manual calculations. An example of the ongoing normalization method as applied to addition is shown below. The addition operation is carried out from right to left; in this case, pence are processed first, then shillings followed by pounds. The numbers below the "answer line" are intermediate results. The total in the pence column is 25. Since there are 12 pennies in a shilling, 25 is divided by 12 to give 2 with a remainder of 1. The value "1" is then written to the answer row and the value "2" carried forward to the shillings column. This operation is repeated using the values in the shillings column, with the additional step of adding the value that was carried forward from the pennies column. The intermediate total is divided by 20 as there are 20 shillings in a pound. The pound column is then processed, but as pounds are the largest unit that is being considered, no values are carried forward from the pounds column. For the sake of simplicity, the example chosen did not have farthings.

## Operations in practice

During the 19th and 20th centuries various aids were developed to aid the manipulation of compound units, particularly in commercial applications. The most common aids were mechanical tills which were adapted in countries such as the United Kingdom to accommodate pounds, shillings, pennies and farthings, and ready reckoners, which are books aimed at traders that catalogued the results of various routine calculations such as the percentages or multiples of various sums of money. One typical booklet that ran to 150 pages tabulated multiples "from one to ten thousand at the various prices from one farthing to one pound". The cumbersome nature of compound unit arithmetic has been recognized for many years—in 1586, the Flemish mathematician Simon Stevin published a small pamphlet called ''De Thiende'' ("the tenth") in which he declared the universal introduction of decimal coinage, measures, and weights to be merely a question of time. In the modern era, many conversion programs, such as that included in the Microsoft Windows 7 operating system calculator, display compound units in a reduced decimal format rather than using an expanded format (e.g. "2.5 ft" is displayed rather than ).

# Number theory

Until the 19th century, ''number theory'' was a synonym of "arithmetic". The addressed problems were directly related to the basic operations and concerned prime number, primality, divisibility, and the Diophantine equation, solution of equations in integers, such as Fermat's last theorem. It appeared that most of these problems, although very elementary to state, are very difficult and may not be solved without very deep mathematics involving concepts and methods from many other branches of mathematics. This led to new branches of number theory such as analytic number theory, algebraic number theory, Diophantine geometry and arithmetic algebraic geometry. Wiles' proof of Fermat's Last Theorem is a typical example of the necessity of sophisticated methods, which go far beyond the classical methods of arithmetic, for solving problems that can be stated in elementary arithmetic.

# Arithmetic in education

Primary education in mathematics often places a strong focus on algorithms for the arithmetic of natural numbers, integers, arithmetic fraction, fractions, and decimals (using the decimal place-value system). This study is sometimes known as algorism. The difficulty and unmotivated appearance of these algorithms has long led educators to question this curriculum, advocating the early teaching of more central and intuitive mathematical ideas. One notable movement in this direction was the New Math of the 1960s and 1970s, which attempted to teach arithmetic in the spirit of axiomatic development from set theory, an echo of the prevailing trend in higher mathematics. Also, arithmetic was used by Ulama, Islamic Scholars in order to teach application of the rulings related to Zakat and Islamic inheritance jurisprudence, Irth. This was done in a book entitled ''The Best of Arithmetic'' by Abd-al-Fattah-al-Dumyati. The book begins with the foundations of mathematics and proceeds to its application in the later chapters.

* * Lists of mathematics topics * Outline of arithmetic * Slide rule

## Related topics

* Addition of natural numbers * Additive inverse * Arithmetic coding * Arithmetic mean * Arithmetic number * Arithmetic progression * Arithmetic properties * Associativity * Commutativity * Distributivity * Elementary arithmetic * Finite field arithmetic * Geometric progression * Integer * List of important publications in mathematics * Mental calculation * Number line

# References

* Cunnington, Susan, ''The Story of Arithmetic: A Short History of Its Origin and Development'', Swan Sonnenschein, London, 1904 * Leonard Eugene Dickson, Dickson, Leonard Eugene, ''History of the Theory of Numbers'' (3 volumes), reprints: Carnegie Institute of Washington, Washington, 1932; Chelsea, New York, 1952, 1966 * Leonhard Euler, Euler, Leonhard,
Elements of Algebra
', Tarquin Press, 2007 * Henry Burchard Fine, Fine, Henry Burchard (1858–1928), ''The Number System of Algebra Treated Theoretically and Historically'', Leach, Shewell & Sanborn, Boston, 1891 * Louis Charles Karpinski, Karpinski, Louis Charles (1878–1956), ''The History of Arithmetic'', Rand McNally, Chicago, 1925; reprint: Russell & Russell, New York, 1965 * Øystein Ore, Ore, Øystein, ''Number Theory and Its History'', McGraw–Hill, New York, 1948 * André Weil, Weil, André, ''Number Theory: An Approach through History'', Birkhauser, Boston, 1984; reviewed: Mathematical Reviews 85c:01004